Recently, advance in biomedical microelectronics has greatly improved in-vivo physiological research, for example, the studies of principles and methods of the neural conduction, which may favor the neurological diagnosis and treatment. The microelectrode array, or MEA for short, not only has fine puncturing ability but also can record in-vivo electrophysiological signals. Therefore, MEA plays a very important role in the field of neural science. Further, MEA also functions as an intermediary between analog physiological signal and bio signal analysis.
A conventional planar MEA cannot fully record the electrophysiological signals. Thus, a 3D MEA is used to detect neural signals. In detection, MEA punctures tissue before detecting actional potentials of neuron, which may cause the damage or infection of tissues. Further, the neural signals from neurons need complicated time-consuming signal processing and computation. Therefore, MEA needs a long-time stability and biocompatibility.
The current MEA usually has a hard-material neural interface, such as a silicon-based material used for the neural interface. If a hard material inserted into the tissues for a long time, the mechanical mismatch between the hard material and the soft tissues may cause inflammation. The heartbeat or breath causes the pulsed movement of the tissues. The pulsed movement further results in micromotion and accelerate inflammation. Inflammation will cause neuroglia to cover the electrodes and form sheath. Thus, the electrodes are insulated from the sheath and hard to record neural signals.
MEA was made by a soft material which was not only harm tissues less but also has the advantages as follow, a excellent biocompatibility, a high signal-to-noise ratio (SNR), a low material cost, and a high suitability for long-time detection.
In Journal of Micromechanics and Microengineering, vol. 14, pp. 104-107, 2004, the Takeuchi et al. proposed a self-assembled “3D Flexible Multichannel Neural Probe Array”, wherein a nickel layer is coated on a planar polymeric probe array to form a nickel layer functioning as a magnetic material. Magnetic force attracts the nickel layers to assemble the planar polymeric probe into a 3D probe array, wherein the thicker nickel layers contribute their strength to the puncturing actions. However, nickel is toxicant to organisms. Further, magnetic force is harder to control the angle of the probe. Thus, the prior art has only limited application.